Dovetailing machine



u y 1959 E. A. STOUTEN ETAL DOVETAILING MACHINE Filed July 9, 1956 7 Sheeis-Sheet 1 ao 7a ooooooooooooooooo F 4| LNVENTORS w. BY SYLVESTER K. BEACH ATTORNEY DOVETAILING MACHINE Filed July 9, 1956 7 Sheets-Sheet 2 ii. 5 TI 57g 20 27 I I I IVLA Q 48 57: l -57$- if 58 T F i q 5 r1 29/ I INVENTORS sowm A. STOUTEN BY SYLVESTER K BEACH fla 1; x. am;

AT TORNEY E. A. STOUTEN ETAL 2,893,450

DOVETAILING MACHINE July 7, P959 7 Sheets-Sheet 3 Filed July 9, 1956 INVENTO EDWIN A. STOUTEN SYLVESTER K. BEACH 8. 1 44" ATTORNEY July 7, 1959 E. A. STOUTEN ETAL DOVETAILING MACHINE 7 Sheets-Sheet 4 Filed July 9, 1956 NVENTO EDWIN A. STOUT N SYLVESTER BEACH BY TTORNEY July 7, 1959 E. A. STOUTEN ETAL 2,893,450

DOVETAILING MACHINE INVENTORQ w ESTER K. BEACH r Z 7 y fi ATTORNEY July 7, 19 9 E. A. STOUTEN ET AL 2,893,450

DOVETAILING MACHINE 7 Sheets-Sheet 6 Filed July 9, 1956 m N E V. m M mu N N Wm H s R T E T W A 9 A W ww aw D Y ES ELL .5.-

United States Patent Ofifice 2,893,450 Patented July 7, 1959 DOVETAILING MACHINE Application July 9, 1956, Serial No. 596,785

5 Claims. (Cl. 14487) This invention relates to the construction of machines used to cut a series of mortise-and-tenon joints along the meeting edges of joined pieces of wood. The series of projections on the piece interengaged with recesses on the other produces the well-known dovetail joint, which presents a firm interlock between the pieces and provides a vastly increased area for the adhesive action of glue over that of the ordinary butt joint. In years past, the dovetail joint was laboriously carved by skilled craftsmen, which limited its use to the exclusively highquality field of furniture, or to other similar types of woodworking. Machines have been developed, however, for the rapid and accurate cutting of both components of the dovetail joint; andthe structural desirability of such a joint has resulted in its wide utilization, even in products of moderate cost.

The conventional dovetailing machine is based upon a series of rotating cutters mounted on a frame, with the cutters being positioned to cut either the projecting tenon or the mating recess. Ordinarily, the machine will be set to cut either one or the other, and the cutters will be driven by suitable power transfer means at high enough speed to generate a proper cutting action in the wood without excessive splintering. The, long period over which these machines have been used has resulted in the development of cutters that may be used to cut either the projection or the recess into which the projection enters. The adjustment of the machine to accommodate either of the two cutting operations is therefore merely a matter of positioning the work pieces and determining their path of movement with respect to the cutters.

Conventional practice in the design of dovetailing machines provides for the mounting of the cutters for rotation on axes fixed with respect to the frame of the machine. The clamping devices for holding the work pieces in position are accordingly mounted in such a fashion that the entire clamp is moveable with respect to the cutters, and means are provided for causing the clamp to follow a predetermined path of movement with respect to the cutters to generate the necessary pattern in the work pieces as they are brought into engagement with the cutters.

The manual manipulation of a clamping table through the desired path of movement is well known. Applicanthas developed a positioning mechanism which can be incorporatediinto relatively conventional dovetailing machine design for accurately and reliably establishing the relative movement of work pieces with respect to the cutters, and which is entirely automatic in its operation. The several features of this system render the machine easily adaptable to various shapes of the dovetail components.

The preferred form of the invention is adapted to operate in conjunction with 'a type of dovetailing machine in which the moveability of the clamping member with respect to the cutters is obtained through the use of a compound system based upon the action of trans-.

Versely-arranged guideways. One guideway is fixedwith respect to the frame, and a sliding member mounted on the guideway is free to move in either of opposite directions along the guideway. That sliding member is itself provided with a guideway arranged transversely with respect to the guideway first mentioned, and a second sliding member is mounted for movement with respect to the first sliding member. An infinite number of serpentine paths of movement can be generated as a combination of the various movements along the transversely-arranged guideways. The determination of the path of movement within the freedom provided by the transverse guideways is the subject of this invention.

The forces responsible for determining any path of movement are provided by the action of closely-related rotary cams. One of these cams operates in conjunction with a follower secured to the first sliding member, and the other cam controls a cam follower mounted on the second sliding member. It is important to note that the cam follower mounted on the second sliding member is designed in such a fashion that it remains in contact with the cam over the full stroke of movement of the device. The action of the related cams,

coupled with biasing springs which maintain the engagement of the followers with the cams, results in a condition in which any particular cam position of one sliding member is associated with a particular position of the other. The complete path of movement is therefore ac curately controlled, and the velocity of movement of the workpiece with respect to the cutters becomes merely a matter of appropriate formation of the cams. The construction details of the machine serve to position the cams for ready access so that the installation and removal thereof is made with a minimum of effort.

The cam system referred to above, coupled with a suitable source of power, makes possible the use of an automatic cycling system which maintains constant control over the path and velocity of movement of the clamp- 1 clamping mechanism as well as the control of the power delivered to the cam positioning system.

Since one of the members of the dovetail joint is ordinarily machined in a position generally parallel to the plane of the axes of the cutters, it is often desirable to 1 adjust the position of the clamp responsible for holding such work pieces so that the clamping members themselves can be placed as close as possible to the ends of the cutters to eliminate chipping or breakout of the wood fibers as much as possible. The occasional need -for adjusting the position of the cutters with respect to the frame to determine the depth of cut will necessitate a corresponding alteration of the position of the clamping surfaces. The invention provides a clamping mechanism which makes unnecessary the alteration of the position of the mechanism responsible for applying clamping force, and provides for the adjustability of clamping plates which are themselves moveable with respect to the actual force-applying system. In this arrangement, the problem of altering the position of the clamp is vastly reduced over that which would exist if the entire forceapplying mechanism had to be repositioned every time the position of the cutters was changed with respect to the frame.

The several features of the invention will be analyzed in detail through a discussion of the particular embodivertical position.

Figure 2 presents a fragmentary section on an enlarged scale from that of Figure 1, and showing the positioning and clamping mechanism in side elevation.

Figure 3 is a fragmentary section in front elevation, illustrating the power-transfer portion of the mechanism shown in Figure 2.

Figure 4 presents a plan view of the power-transfer and cam mechanism. Portions of one of the sliding members constituting the compound are illustrated in Figure 4, with the other being removed for clarity of presentation.

Figure 5 is a section taken on a plane 55 of Figure 3.

Figure 6 is an exterior side elevation of the machine shown in Figure 1.

Figure 7 presents a schematic diagram showing the cycling system for controlling the operation of the machine.

Figure 8 illustrates the relationship of the path of movement of the workpiece with respect to the rotating cutters in the cutting of two back-to-back tenon sections.

Figure 9 shows the two pieces cut at the same time in the fashion presented in Figure 8.

Figure 10 presents an assembled dovetail joint.

Figure 11 illustrates the components of the joint shown in Figure 10, but separated to show the details of the mortise and the tenon sections.

Figure 12 presents a sectional side elevation, taken on the line 12-12 of Figure 13, of a modified form of the machine in which the vertical clamping mechanism has been removed.

Figure 13 presents an exterior plan view of the machine shown in Figure 12.

Figure 14 presents a perspective view of the upper sliding member of the clamping system.

Referring particularly to Figures 1 and 2, the frame of the machine is provided with lugs as shown at 21 and 22 in Figure 1 to which the rectangular sub-frame 23 is bolted. A lower group of bearing blocks 24 and an upper group 25 provide for the rotatable mounting of the spindles 26 which drive the cutters 27. The spindles are driven in groups of 5 by the arrangement best shown in Figure 12. A motor 28 is mounted on the frame 20, and drives the counter shaft 29, through the belt 30 and the pulley 31. The shaft 29 carries a series of bevel gears, one of these being indicated at 32 in Figure 12, and each of which meshes with a beveled gear 33 driving a vertical shaft 34 supported by the lower bearing blocks 35 and the upper sleeve bearing units 36 and 37. The sleeve bearing units 36 and 37 are fixed with respect to the rectangular sub-frame 23. The gears 38 and the mating gears 39 are preferably of the helical type, with the gear 39 representing the central spindle of a group of 5. The two spindles adjacent to the central spindles on either side are driven as idlers. Reference to Figure 1 indicates the manner in which the gears 39 of the group of spindles indicated at 40 is offset axially from the gears of the adjacent group 41 to provide clearance.

yThe angle brackets 42 (refer to Figure 1) are provided with slots 43 which are engaged by bolts 44 for securing the angle brackets in position with vertical adjustability. A locating plate 45 is fixed with respect to the brackets 42, and has a comb-shaped inner edge (refer to Figure 2) arranged with the teet 46 extending between the' cutters 27. When work pieces are in the vertical position shown at 47 in Figure 2, the upper surfaces of the comb portion serve as stops determining the position to which the work pieces are inserted prior to being clamped in position. In the modification of the machine shown in Figure 12, a comb-shaped member is also formed as part of the channel-shaped piece 50 secured to the clamping mechanism by the angle bracket 51 and bolts as shown at 52 and 53.

The clamping mechanism of the machine is slideably mounted on the guide rods 55 and 56 which are fixed 4 with respect to the frame 20. (Refer to Figures 2, 4, and 12.) A sliding member 57 engages the rods 55 and 56, with the bearing sleeves 58 and 59, and carries a set of guide rods 60 and 61 arranged perpendicularly to the plane containing the axes of the cutters 27.

The construction of the sliding member 57 involves the two similarly shaped spaced plates 57a and 57]), each of which is provided with bearing sleeves as shown at 58 and 59 in Figure 2. The plates 57a and 57b are connected by a cross bar 570 having the principal function of assuring that the end plates move along the guide rods 55 and 56 in unison. The upper sliding member 62 is provided with hearing blocks as shown at 63 and 64 in Figure 2 which engage with rods 60 and 61, and provide for sliding movement of the jaws of the clamp toward and away from the cutters. This movement, combined with the movement parallel to the cutters provided by the guide rods 55 and 56, permits the clamp system a limited freedom of movement in all horizontal directions, with respect to the cutters.

The upper sliding member 62 has an underslung portion 65 having a central area 66 inclined upwardly to the horizontal in a direcion proceeding toward the cutters 27 The structural details of the upper sliding member 62 are best shown in Figure 14. When the upper and lower sliding members are in assembled condition, a spring 57d acts between a ring 57e and the bearing block 64 on the upper sliding member to urge the upper sliding memher to the right as shown in Figure 2. This structure is duplicated on opposite sides of the machine. A wedgeshaped member 67 (refer to Figure 12) is adjustably secured in position on the surface 66 by bolts as shown on 68, and movement of the member 67 along the surface 66 will serve to raise and lower the supporting surface on which the Work pieces 49 rest.

The adjustment of the wedge member '67 along the surface 66 is preferably accomplished through the action of the bolts 57g mounted on the brackets 57h secured to the portion 65 of the upper sliding member 62. After the proper adjustment has been secured, the bolt 68 may be tightened to lock the established relationship.

An arch-shaped frame 69 is provided at its opposite ends with mounting brackets as shown at 70 in Figure 12, andis secured at the feet of these brackets to the upper sliding member 62 by bolts as indicated at 71 and 72 in Figure 2. The spaced vertical air cylinders 73 drive piston rods 74 on which the clamping shoe 75 is mounted. Vertical movement of the rods 74 under the action of the air cylinder assemblies 73 will serve to apply a clamping action forcing work pieces 49 against the upper surface of the wedge-shaped member 67.

A system for clamping work pieces in a vertical position is shown in Figure 2. A set of air cylinders 76 at the opposite ends of the arch frame 69 drive the piston rods 77 which carry between them the clamping shoe 78. The shoe is secured to the end of the piston rod 77 by nuts as shown at 79 in Figure 2. The pair of plates 80 and 81 are secured against lateral displacement with respect to each other by bolts as shown at 82 at the four corners of the plates. These bolts solidly engage the inner plate 81, and slideably engage the outer plate 80. Springs as indicated at 83 surround each of the bolts 82, and generate a biasing efiect tending to separate the plates 80 and 81'. The heads of the bolts 82 limit the degree of separation under the urging of the springs 83 when the plates arenot under the confinement of the clamping shoe 78.. The plates 80 and 81 constiutte a relatively independent sub-assembly which is positioned with respect to the arch frame 69 by the bracket 84. A bolt 85 operates as astop which determinesthe vertical position of the sub-assembly including the plates 80 and 81 as they are inserted between the clamping bar 78 and the forward face of the arch frame 69. While the clamping 'sho'e' 78 has a fixed horizontal position, adjustment of the bolt -85 will permit the lower edges of the clamping plates 80 and 81 to he moved vertically with respect to f the cutters 27 to maintain the proper relative position thereof.

The clamping system in its entirety is caused to followv a pre-determined path of movement through the action of the cams 86 and 87 which bear respectively against the cam followers 88 and 89. (Refer to Figures 2, 3, 4, and 5.) The carn i'ollower 89 is mounted on the bracket 90 secured to the lower sliding member 57 by the bolt and nut assembly 91. Rotation of the cam 87 will therefore impart movement of the lower sliding member 57 (and all of the structure carried by it) along the guide rods 55 and 56.

The cam follower 88 is adjustably mounted on the bracket 92 with the nut 93; and the bracket 92 is fixed with respect to the underslung portion 65 of the upper sliding member 62. Rotation of the cam 86 will therefore impart movementof the-upper sliding member 62 along the guide rods 60 and 61, regardless of the lateral position of the lower sliding member 57 along the guide rods 55 and 56. The cam follower 88 is formed to have sufl icient length to remain in contact with the cam 86 over the entire range of movement of the clamping :system induced by the cam 87.

Power for the operation of the cams 86 and 87 is derived from the motor 94, mounted on the adjustable lbracket 95 supported by the frame 20. The motor 94 drives a belt 96 which transfers power to the pulley 97 :mounted on the shaft 98. A clutch assembly generally indicated at 99 is controlled by a yoke arm 100 pivotedly supported on the frame 20 by the bracket 101. Engagement of the clutch assembly 99 serves to deliver power to the shaft 98 of the speed-reducer unit 102, the output shaft of which drives the sprocket 103 within the gearbox 104. A chain 105 transfers power from the sprocket 103 to the upper sprocket 106 mounted on the shaft 107 which drives the cam 86. A bevel gear 108 on the shaft 107 meshes with a similar bevel gear 109 mounted on the shaft 110, and supporting the cam 87. A separate cam 111 is also mounted on the shaft 110 for the actuation of the switch unit 112 mounted on the bracket 113 fixed with respect to the frame 20 (through attachment to the gear box 104). The bevel gears 108 and 109 operate on a one-to-one ratio, resulting in maintaining a constant relationship between the angular positions of the cams 86 and 87.,

. The system for controlling the working parts of the device is best illustrated in the schematic diagram presented in Figure 7. The yoke arm 100 controlling the clutch 99 is positioned by the air cylinder 114 mounted on the frame 20. The compressed air conduit 115 conducts compressed air from one end of the 2-position solenoid control valve 116; and in the position illustrated in Figure 7, the compressed air from the supply line 117 is delivered on the sideof the piston of the air cylinder 114 which will move the piston to the left, and generate the illustrated position of the yoke arm 100 to cause disengagement of the clutch 99. The valve 116 has been positioned as shown as a result of the energizing of the solenoid 118 by the switch 112 momentarily closed by the cam 111. The inertia of the machine will ordinarily serve to carry the cam beyond the momentary closure of the switch 112 so that the contacts remain normally open. To start the cycle of. operation of the machine, the foot-control switch 119 is depressed, which energizes the solenoid 120. The valve 116 is then moved to the opposite position from that indicated in Figure 7, moving the plunger 121 to a position in which the line 115 is blocked. Until this action takes place, the vertical clamping cylinder 73 and the horizontal clamping air cylinders 76 will be receiving pressure on the side tending to drive their respective pistons upwardly and outwardly-torelease all clamping action, as a result of communication of the air cylinders through the lines 7 5'; along said frame guideway means, and said first sliding."

122 and 123 with the line 115. When the piston 121 of the valve 116 moves to'the opposite end of the cylin-.

der 116 from the illustrated position, air pressure will no longer be supplied to the opening port of the clamp ing cylinders, and will first be delivered through the lines 124 and 125 to the opposite side of the pistons of the clamping cylinders to create a clamping action for firmly securing the work pieces in position prior to any other action taking place in the machine. At the same instant that air pressure is delivered to generate clamping action, it is supplied to the pneumatic timer unit 126 through the line 127. The timer 126 is a standard piece of equipment, and the details of it form no part of this invention. The net function of the timer unit 126 is to delay the delivering of air pressure through the line 128 until a sufiicient period has elapsed for the full generation of clamping pressure at the air cylinders 73 and 76 to assure that the work pieces are properly held before the cutting operation of the machine begins. After the required lapse of time has taken place, air pressure supplied through the line 128 causes the air cylinder 114 to rock the yoke arm in counterclockwise direction and to engage the clutch 99. Such action instantly begins the rotation of the shaft 98, and the corresponding, The clamping.

rotation of the cams '86, 87, and 111. mechanism is forced to move through its predetermined path of movement as a result of the action of the cams, which continues until the cam 111 causes the switch 112' to close momentarily. On the completion of the cycle determined by the closure of the switch 112, the circuit to the solenoid 118 is again energized, causing the clutch to be disengaged and the clamping mechanism released (preferably in that order). The transformer 129 is used to establish a low voltage circuit (preferably about 12 volts) for supplying the various solenoids of the system. Power is delivered to the transformer 129 through the line terminals 130.

As a result of the operation of the machine, the work pieces can be moved in a path similar to that indicated in Figure 8 with respect to the cutters, when the machine is adjusted to form the tenon portion of the dovetail. With this type of cut, it is preferable to place two work pieces together as shown in Figure 9, and the movement of the machine through its complete path will cause the cutters to generate the required tenon portions on both work pieces at the same time. The mortise, or recess, portions of the mating dovetail elements are ordinarily generated by a straight path of movement of the clamping mechanism bringing the work pieces directly in line into engagement with the cutters, followed by the return along the same line. The two elements of the conventional dovetail are shown separated in Figure 11, and in engagement in Figure 10. The tenon element is indicated at 131, and the mortise element at 132. It is also entirely practical to adjust the machine to cut side and front elements at the same time, instead of two of each. The cutters are then positioned between the workpieces, one of which is clamped horizontally and the other vertically. In each cycle of movement, the cutters are engaged first by one piece and then by the other.

The particular embodiments of the present invention when have been illustrated and discussed herein are for illustrative purposes only and are not to be considered as a limitation upon the scope of the appended claims. In these claims, it is our intent to claim the entire invention disclosed herein, except as we are limited by the prior art.

We claim:

1. A dovetailing machine comprising: a frame; a plurality of cutters mounted for rotation on parallel axes fixed with respect to said frame; guideway means mounted on said frame and disposed parallel to a plane perpendicular to the axes of said cutters; a first sliding member,.

said first sliding member being mounted for movement member having, guideway means disposed transverselywith respect tosaid frame guideway means; a second sliding member, saidsecond sliding member being mounted for movement'on said first sliding member guideway means; firstvcam means, said first cam means being mounted for rotation with respect to said frame on an axis substantially perpendicular to a plane parallel to said frame guideway means;second cam means, said second cammeans being mounted for rotation with respect to saidframeon an axis perpendicular to a plane parallel to said first'sliding, member guideway means; power transfer means establishing a constant relationship between the angular positions of said first and second cam means, said power transfer means including intermeshed gears on mutually perpendicular shafts respectively supporting said first and second cam means; first and second cam-follower means mounted on said first and second sliding members, respectively, and respectively engaging said first and second cammeans, said second cam follower means being of sufiicient length to remain in engagement with said second cam means over the full stroke ofrnovement induced by said first cam means; first and second biasing means respectively urging said first and second sliding members in opposition to said first and second cam means; and work-clamping means mounted on said second sliding member whereby rotation of said cams induces a movement of clamped workpieces in a predetermined path with respect to said cutters.

2. A dovetailing machine comprising: a frame; a plurality of cutters mounted for rotation on parallel axes fixed with respect to said frame; guideway means mounted on said frame and disposed parallel to a plane perpendicular to the axes of said cutters; a first sliding member, said first sliding member being mounted for movement along saidframe guideway means, and said first sliding member having guideway means disposed transversely with respect to said frame guideway means; a second sliding member, said second sliding member being mounted for movement on said sliding member guideway means; first cam means, said first cam means being mounted for rotation with respect to said frame on an axis transverse to said frame guideway means; second cam means, said second cam means being mounted for rotation with respect to said frame on an axis transverse to said first sliding member guideway means; power transfer means establishing a constant relationship between the angular positions of said first and second cam means; first and second cam follower means mounted on said first and second sliding members, respectively, and respectively engaging said first and second cam means, said second cam follower means being of sufficient length to remain in engagement with said second cam means over the full stroke of movement induced by said first cam means; first and second biasing means respectively urging said first and second sliding members in opposition to said first and second cam means; work-clamping means mounted on said second sliding member whereby rotation of said cams induces a movement of clamped workpieces in a predetermined path with respect to said cutters; and control means for energizing said Workclamping means in response to the angular position of said cam" means.

3. A dovetailing machine comprising: a frame; a plurality of cutters mounted for rotation on parallel axes fixed with respect to said frame; guideway means mounted on said frame and disposed parallel to a plane perpendicular to the axes of said cutters; a first sliding member,

said first sliding member being mounted for movement along said frame guideway means, and said first sliding member having guideway means disposed transversely with respect to said frame guideway means; a second sliding member, said second sliding member being mounted for movement on said first sliding member guideway means; first cam means, said first cam means being mounted for rotation, with respect to said frame on an axis substantially perpendicular to a plane parallel to said frame guideway. means;'second cam means, said cam means; first and second cam follower means mounted on said first and second sliding. members, respectively, and respectively engaging said first and second cam means, said-second'eam follower means being of sufficient length to remain in engagement with said second cam means over the full stroke of movement induced by said first cam means; first and secondbiasing means respectively urging said first and second slidingmembers in opposition to said first and second cam means; and work-clamping means mounted on said second sliding member whereby rotation of said cams induces a movement of clamped workpieces in a predetermined path with respect to said cutters.

4. A dovetailing machine comprising: a frame; a plurality of cutters mounted for rotation on parallel axes fixed with respect to said frame;.guideway means mounted on said frame and disposed parallel to a plane perpendicular to the .axes of said cutters; a first sliding member, said first sliding member being mounted for movement along said frame guideway means, and said first sliding member having guideway means disposed transversely with respect to said frame guideway means; a second sliding member, said second sliding member being mounted for movement on said first sliding member guideway means; first cam means, said first cam meanscam means; first and second cam follower means mounted on said first and second sliding members, respectively, and respectively engaging said first and second'cam means,

said second cam follower means being of sufficient length to remain in engagement with said second cam means over the full stroke of movement induced by said firstcam means; first and second biasing means respectively urging said first and second sliding members in opposition to said first and second cam means; and workclamping means mounted on said' second sliding member whereby rotation of said cams induces a movement of clamped workpieces ina predetermined path with respect to said cutters.

5; A dovetailing machine comprising: a frame; a plurality of cutters mounted for rotation on parallel axes fixed With respect to said frame; guideway means mounted on saidframe and disposed parallel to a plane perpendicular'to the axes of said cutters; a first sliding member, said first sliding member being mounted for movement along saidframe guideway means, and said first sliding member having, guideway means disposed transverselywith respect to said frame guideway means; a second sliding member, said second sliding member being mounted for movement on said first sliding member guideway means; first cam means, said first cam means being mounted for rotation with respect to said frame on an axis transverse to said frame guideway means; second cam. means, said second cam means being mounted for rotation with respect to'said frame on an axis transverse to said first sliding member guideway means; power transfer means establishing. a constant relationship between the angular positions ofsaid, first and second cam means; first and secondcam follower means mounted on said first and second sliding members; respectively, and respectively engaging said-first and second cam means, said.

10 second cam follower means being of suflicient length to References Cited in the file of this patent remain in engagement with said second cam means over UNITED STATES PATENTS the full stroke of movement induced by said first cam 2 225 263 Farrell D e 17 1940 means; and Work-clamping means mounted on said second 2260662 Farrell Oct 1941 sliding member whereby rotation of said cams induces a 5 2:299:6O2 Teague Oct 20 1942 movement of clamped workpieces in a predetermined 2,606,581 Weisner Aug 12, 1952 P with respect to Said cutters- 2,607,375 Gillespie Aug. 19, 1952 

